"We are confident that, together with our labor partners, we will continue to provide stellar service to our valued customers and community," said Port of Tacoma CEO John Wolfe in a statement. "In doing so, will continue to realize new business opportunities at the Port of Tacoma."

The service will leave the Port of Seattle’s Terminal 18, which is owned by SSA Marine, based in Seattle.

"It is important that the business remains in Washington,” the statement said. “Unfortunately, though many of the jobs will be preserved, others may not. Some who work in the Seattle harbor could see their livelihood impacted severely or in some cases, disappear.”

The change could reverse the Port of Seattle’s current cargo lead over the Port of Tacoma, after some years when Tacoma was ahead.

In 2011, the Port of Tacoma handled the equivalent of 1.49 million 20-foot containers, a measurement called TEUs, according to port statistics. The Port of Seattle handled 2.03 million TEUs during the same period.